Production of fluoroacetic acids



Patented May 2, 1950 UNITED ISTATES PATENT OFFICE PRODUCTION OF FLUOROACETIC ACIDS "John W. 0. Crawford, Welwyn Garden City, and Eric R. Wallsgrove, Leamington Spa, England, Massignors to Imperial Chemical Industries Lim- -ited,lalcorporation of Great Britain N oBrawing. :Appli'cation February 10,1948, Se-

.;: .1]1i;;l7No. 7;527. In: Great Britain,.February 17,

11 Claims.

:This" process suffers from :the" disadvantage that it cannot be accomplished satisfactorily-in stainless steel pots '2 as these: :pots are attacked by hot l alkaline permanganate l solutions. accomplished in enamel=lined pots erg. Pfaudler It cannot-"be pots; either ift strong :GHil'lSlllCi alkalitsolutions are used as these solutions attack -the linings of these wpots. Iffhowever, lther reaction is accomplished in-the presence rofr a small amount of alkali, car- :bon dioxide iisdiberatedduring the reaction-and this 1 carries 1 some fluoroacetic acid-fromethe: reaction mixture i-and processing complications or -loss of yield result.

1 It has also been-proposed to-produce trifiuoroacetic acid by. the vchromia acid oxidation of maminobenzotrifluoride. This latter process, howevery-has xthe disadvantage: ofebeing slows costly,

, givings only yields t l theuorder of 55-60 ,a-and presenting major corrosion problems. l r An object of this invention is to provide means for the productionmof fiuoroacetiomacids, esters and salts thereof bya process suitable for use in "enamel lined' 'vessels; F AliOflhEI obj set is topro- Vide an ec'onomicmeans for" the production of fluoroacetic" acids; esters 'andzisalts thereof; A

further object "is to provide means for the rpm- 'duction' of fiuoroa'cetic" acids; esters "and salts Ilthereofbyau'process giving'greater yieldsand taking"lessthnethanheretofore. 1 Other' objects willappearhereinariter.

l z'According to-the=present" invention these ob- 'ijects are accomplishedby" airprocess'comprising "the step ofreacting a fluoro'ethylenic' compound "of the' type"CF2XGY CYZ'in whichX is'hydrogen, fluorine or'chlorinef'Yis hydrogen or' chide or hydroxide to combine with all acidsliberated by'the reaction. "'These reactiorr *mixtures have a low-'- 'alkaliiiity an'd the enameuea glasslined vessels are not attacked, as is the case where ...c1ude 3,3,3-trifluoro-LL2,

.thehnecessary alkali is provided by the alkali J'netal. hydroxides; Fluoroacetic acidsmay be obtained by acidifying .mixtures obtained-after this reactionlor fractionsvof these mixtures).

, Fluoroethylenic compounds in which Z is CFzX are particularly preferred as thesegive a yield per mol of permanganatetwice that of, the other fluoroethylenic compounds usedas starting ma- .7 terials in the process of this invention.

l Suitable starting materials which may beused in carrying out the process ofouiiinvention intrichloro-propene-l '1.CFs--CCl=CCl2, 3;3I-difiuoro-1,l,2;3-tetrach1orolpropene-l,iCClFz-CCl=CC12 and l,1,1,4,4,4-

, hexafluoro-2,3 dichloro-butadiene-2,

- Calcium hydroxide is preferred on account of its availability and cost and because, if any permanganate remains'in the reaction mixtureat the competition of the reaction, this is destroyed easilyby passing sulphur dioxide, manganese di- .oxide and calcium sulphate being precipitated 1, from solutions containing calcium hydroxide.

"*Any' salts of permanganic acid may be used in the process of thisinvention. Potassium perymanganate is, preferred as it is available and 'cheap. The use of calcium permanganate in conjunction with calciumhydroxide andwith the use of sulphur dioxide todestroy the excess per manganate gives solutions of salts of fluoroacetic acids which are contaminated only with calcium ..chloride.

' The 'perma-nganate saltmay be used in the .qttheoretical-amount or in slight excess and may be, forexample in the form of a 5% to 25% aqueous solution and of these the more concentrated "solutions are' preferred because less water has to be removed subsequently.

i. In general; temperatures ofgthe order of C.

'to80.C; are-satisfactory forcarrying out the process ofithisinvention although awider range of temperatures may be employed, for example, temperatures ranging from 20 (3., to 130 C., In

" general, theprocessmay be carried outat atmospheric pressure althoughhigher or lower pressures may be employed 'if desired. ,When temperatures above "C. are, employed, pressure vessels may be used, and the permanganate and alkali may be addedwsimultaneously and slowly to the higher boiling organic start-materials. An

alternative procedure which is preferable in some oases-is to add the-organic compound to an agitated solution --containingpermanganate and al- *kali. r

asoaoes In one form of the invention the fluoroethylenic compound is charged into a reaction vessel, with water, calcium or potassium permanganate and sufilcient lime to ensure that the reaction mixture remains alkaline throughout the reaction. The mixture is heated with agitation, the temperature being raised sufiiciently to produce smooth reaction.

When the reaction has been completed any unreacted fluoroethylenic compound may be distilled 01f. If there is present excess of permanganate, it may be destroyed by reaction with a reagent such as sulphur dioxide, hydrogen peroxide, sodium sulphite, sodium bisulphite or sodium hydrosulphite. The salt of the fiuoroacetlc acid may be isolated admixed with calcium chloride and potassium chloride, if potassium permanganate is used, from the reaction mixture by filtration to remove manganese dioxide, calcium sulphate, calcium carbonate and any unreacted lime, and evaporation to dryness. An alternative method of isolating salts other than those of the alkaline earth metals is to treat the reaction mixture with a water-soluble carbonate, such as sodium or potassium carbonate, and filter off the solution of the crude salt from precipitated calcium carbonate. If desired, the filtered reaction mixture may be treated with the theoretical amount of an excess of sulphuric acid to set free the fiuoroacetic acid, the aqueous fluoroacetio acid distilled off, neutralised with sodium carbonate and dried as the sodium salt, which may be mixed with the theoretical amount or an excess of sulphuric acid (suitably of 93% to 100% strength), and the fiuoroacetic acid recovered by distillation.

Alternatively the acid may be obtained from the neutralised reaction mixture, which may have been treated with a soluble carbonate, if desired, by evaporation followed by extraction of the fluoroacetates with an organic solvent, evaporation of the organic solvent, treatment with the theoretical quantity or an excess of sulphuric acid and distillation of the pure fiuoroacetic acid. Any organic solvent which is inert to the ingredients of the reaction mass and which dissolves the desired product but not the undesired products such as the halide salts, may be used. Examples of satisfactory solvents are methyl alcohol, ethyl alcohol, isopropyl alcohol, secondary butyl alcohol, diethyl ether, acetone, dioxane and ethyl acetate.

Esters are prepared from the salts and acids produced by the process of this invention by any of the conventional methods for example direct esterification, ester interchange and the like. Thus in one method of preparing esters of any excess of permanganate in the oxidised reaction mixture is destroyed, the precipitated manganese dioxide filtered off and the filtrate evaporated to dryness, sulphuric acid and the alcohol to be es- :erified added and the ester recovered by distillaion.

The following examples in which all parts are by weight, except where otherwise stated illustrate the process of this invention but it is to be understood that the invention is in no way limited by the examples.

Example I The potassium permanganate was dissolved in the water and fed into the reaction vessel together with the calcium oxide. The trichlorotrifiuoropropene was added to the well-stirred solution at -'70 C. over a period of 9 hours. After completion of the addition, the solution was gradually heated up to 95 C. until no further refluxing took place. fter cooling, the solution was decolourised by addition of sodium bisulphite and the precipitated manganese dioxide, calcium sulphate and calcium carbonate were filtered oif. The filtrate was treated with strong potassium carbonate solution until no more calcium carbonate was precipitated. After filtration, the solution was evaporated to dryness and extracted with methanol, giving 2'7 parts (89% yield) of potassium trifluoroacetate.

Example 11 95 parts of trifluorotrichloropropene were oxidised as in Example 1.

136 parts of crude dry solid were obtained by evaporation. i7 parts of this solid were treated with 32 parts of concentrated sulphuric acid which was added gradually. When all the acid had been added, the mixture was heated and the trifiuoroacetic acid distilled oil as it was formed. The crude product was redistilled and 9 parts of trifiuoroacetic acid, B. P. '71.5-72.5 0., containing less than 0.03% hydrochloric acid were obtained.

We claim:

1. A process for the production of potassium trifluoroacetate which comprises reacting trifiuoro trichloro propene at a temperature of 65-70" C. at atmospheric pressure with an aqueous potassium permanganate solution of 53-25% concentration in the presence of sufficient calcium hydroxide to combine with all of the acids liberated during the reaction, cooling the reaction mixture. decolorizing the mixture bv addition of sodium bisulfite, filtering the solution, treating the filtrate with potassium carbonate until calcium carbonate ceases to be preci itated, filtering the resulting mixture, evaporating the filtrate to dryness and extracting the dry mass with alcohol, whereby potassium trifiuoroacetate is obtained.

2. A process for the production of a fluoroacetyl compound which com rises the step of reacting a fiuoroethylenic com ound from the group consisting of those having the general formulae:

CF2XCY=CYZ and CF2XYC=CYCF2X wherein X is a radical from the group consisting of hydrogen, fluorine and chlorine, and Y and Z Parts 3,3,3-trifiuoro-1,1,2 triohloropropene-1 40 Calcium hydroxide 27 Potassium permanganate 46 Water 300 are radicals from the group consisting of hydrogen and chlorine, with an aoueous metal perman anate solution, in the presence of an amount of a basic compound from the grou consisting of calcium and magnesium oxide and h droxide sufficient to combine with all the acids liberated during the reaction, and separating the resulting fiuoroacetyl compound from the reaction mixture.

3. A. process as claimed in claim 2 wherein the aoueous metal perm an anate solution is of 543.5% by we ght concentration.

4. A process as claimed in claim 2 wherein the permanganate solution is an aoueous potassium perman anate solution of 5-25% by weight concentration.

5. A process as claimed in claim 2 wherein said reaction is carried out at a temperature between 20 and C.

6. A process as claimed in claim 5 wherein said 5 reaction is carried out at a temperature of 70-80 C.

7. A process as claimed in claim 2 wherein said reaction is carried out at atmospheric pressure.

8. A process as claimed in claim 2 wherein said reaction is carried out under super-atmospheric pressure and at a temperature greater than 100 C.

9. A process as claimed in claim 2 wherein separation of the fiuoroacetyl compound is accomplished by treating the reaction mixture with a soluble carbonate, filtering, evaporating the filtrate to dryness, extracting the fluoroacetates with an organic solvent and evaporating the solvent.

10. A process as claimed in claim 2 wherein the fiuoroethylenic compound is selected from the group consisting of 3,3,3-trifluoro-1,1,2-trichloropropene-l; 3,3-difluoro l,1,2,3 tetrachloro-propene-l and 1,1,l,4=,4,4-hexafluoro 2,3 dichlorobutene-2.

11. A process for th production of a metal salt of a fluoroacetic acid which comprises reacting a fluoroethylenic compound from the group consisting of those having the general formula:

wherein X is a radical from the group consisting of hydrogen, fluorine and chlorine, and. Y and Z are radicals from the group consisting of hydro gen and chlorine, with an aqueous metal permanganate solution, in the presence of an amount of a basic compound from the group consisting of calcium and magnesium oxide and hydroxide required to combine with all the acids liberated during the reaction, and separating the resulting fiuoroacetyl compound from the reaction mixture.

JOHN W. C. CRAWFORD.

ERIC R. WALLSGROVE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,371,757 Henne Mar. 20, 1945 2,414,706 Babcock et al Jan. 21, 1947 OTHER REFERENCES Henne et al., J. Am. Chem. Soc., vol. 67, pp. 918- 919 (1945) 

2. A PROCESS FOR THE PRODUCTION OF A FLUOROACETYL COMPOUND WHICH COMPRISES THE STEP OF REACTING A FLUOROETHYLENIC COMPOUND FROM THE GROUP CONSISTING OF THOSE HAVING THE GENERAL FORMULAE: 